In a wireless communications system such as a mobile cellular communications system, a wireless local area network (WLAN) system, or fixed wireless access (FWA) system, communications nodes such as a base station (BS) or an access point (AP), a relay station (RS), and user equipment (UE) usually have capabilities of transmitting their own signals and receiving a signal from another communications node. Because a radio signal attenuates greatly on a radio channel, compared with a signal transmitted by a communications node, a signal from a communication peer end has been very weak when arriving at a receive end. For example, a power difference between a received signal and a transmitted signal of a communications node in the mobile cellular communications system reaches 80 dB to 140 dB or even higher. Therefore, to avoid self-interference from a transmitted signal to a received signal of a same signal transceiver, radio signal sending and receiving are usually performed by using different frequency bands or different time periods. For example, in frequency division duplex (FDD), sending and receiving are performed by using different frequency bands separated by a specific guard band; in time division duplex (TDD), sending and receiving are performed by using different time periods at a specific guard interval. Both the guard band in the FDD system and the guard interval in the TDD system are used to ensure adequate isolation between receiving and sending, so as to avoid interference from sending to receiving.
Different from an existing FDD or TDD technology, a wireless full-duplex technology supports simultaneous receiving and sending operations on a same radio channel. In this case, spectral efficiency of the wireless full-duplex technology is twice as much as that of the FDD or TDD technology theoretically. A premise for implementing wireless full-duplex is to avoid, reduce, and cancel as much as possible strong interference (referred to as self-interference, Self-interference) from a transmitted signal to a received signal of a same signal transceiver, so that the strong interference causes no impact on correct reception of a wanted signal.
In an existing wireless full-duplex system, a DAC (Digital to Analog Converter), an up-converter, and a power amplifier that are on a transmit channel, a low noise amplifier (LNA), a down-converter, and an ADC (Analog to Digital Converter) that are on a receive channel, and the like are functional modules of an intermediate frequency unit of an existing signal transceiver. Cancellation of self-interference from a transmitted signal is completed by a spatial interference suppression unit, a radio frequency front-end analog interference cancellation unit, a digital cancellation interference unit, and the like. In the existing wireless full-duplex system, analog self-interference cancellation is mainly to eliminate an interference signal that passes through a self-interference main path. Digital cancellation interference is a supplement of the analog interference cancellation and is to eliminate, in a baseband, a self-interference signal remaining in a digital received signal.
An existing digital interference cancellation technology is mainly to perform interference reconstruction and cancellation based on a self-interference signal model. However, due to impact of a non-ideal feature of a signal transceiver, a received self-interference signal cannot be absolutely represented by using an ideal signal model and further, cannot be reconstructed or canceled. Therefore, interference cancellation performance of the prior art is limited by the non-ideal feature of the signal transceiver. In an example in which IQ (in-phase quadrature) imbalance exists, in a general communications system, a power of an image interference signal caused by IQ imbalance is 20 dB to 30 dB lower than a main signal power, and therefore, communication can be performed normally in a case in which IQ imbalance is not eliminated. However, for the existing wireless full-duplex system, because a power of the received self-interference signal is far greater than a power of a wanted signal sent by the communication peer end, and a power difference obtained after radio frequency interference cancellation is performed is still greater than 30 dB, the digital interference cancellation module can ensure normal communication with the communication peer end only after self-interference greater than 40 dB is canceled. However, an existing digital interference cancellation technology cannot effectively cancel an image interference signal caused by IQ imbalance. As a result, the digital interference cancellation technology cannot cancel self-interference greater than 40 dB, and self-interference cancellation cannot be implemented in the wireless full-duplex system.
The existing digital interference cancellation technology cannot effectively implement self-interference cancellation when IQ imbalance exists in a communications system, and digital interference cancellation performance is relatively poor.